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Table of Contents

A collection of SQL examples...

SELECT Queries

SELECT * FROM table_name;

DISTINCT: filters away duplicate values and returns rows of specified column

SELECT DISTINCT column_name;

WHERE: used to filter records/rows

SELECT column1, column2 FROM table_name WHERE condition;
SELECT * FROM table_name WHERE condition1 AND condition2;
SELECT * FROM table_name WHERE condition1 OR condition2;
SELECT * FROM table_name WHERE NOT condition;
SELECT * FROM table_name WHERE condition1 AND (condition2 OR condition3);

ORDER BY: used to sort the result-set in ascending or descending order

SELECT * FROM table_name ORDER BY column;
SELECT * FROM table_name ORDER BY column DESC;
SELECT * FROM table_name ORDER BY column1 ASC, column2 DESC;

SELECT TOP: used to specify the number of records to return from top of table

SELECT TOP number columns_names FROM table_name WHERE condition;
SELECT TOP percent columns_names FROM table_name WHERE condition;

Not all database systems support SELECT TOP. The MySQL equivalent is the LIMIT clause

SELECT column_names FROM table_name LIMIT offset, count;

LIKE: operator used in a WHERE clause to search for a specific pattern in a column

  • % (percent sign) is a wildcard character that represents zero, one, or multiple characters
  • _ (underscore) is a wildcard character that represents a single character
SELECT column_names FROM table_name WHERE column_name LIKE pattern;
  • LIKE 'a%' (find any values that starts with "a")
  • LIKE '%a' (find any values that ends with "a")
  • LIKE '%or%' (find any values that have "or" in any position)
  • LIKE '_r%' (find any values that have "r" in the second position)
  • LIKE 'a%%' (find any values that start with "a" and are at least 3 characters in length)
  • LIKE '[a-c]%' (find any values starting with "a", "b", or "c"

IN: operator that allows you to specify multiple values in a WHERE clause, essentially the IN operator is shorthand for multiple OR conditions

SELECT column_names FROM table_name WHERE column_name IN (value1, value2, ...);
SELECT column_names FROM table_name WHERE column_name IN (SELECT STATEMENT);

BETWEEN: operator selects values within a given range inclusive

SELECT column_names FROM table_name WHERE column_name BETWEEN value1 AND value2;
SELECT * FROM Products WHERE (column_name BETWEEN value1 AND value2) AND NOT column_name2 IN (value3, value4);
SELECT * FROM Products WHERE column_name BETWEEN 01/07/1999 AND 03/12/1999;

NULL: values in a field with no value

SELECT * FROM table_name WHERE column_name IS NULL;
SELECT * FROM table_name WHERE column_name IS NOT NULL;

AS: aliases are used to assign a temporary name to a table or column

SELECT column_name AS alias_name FROM table_name;
SELECT column_name FROM table_name AS alias_name;
SELECT column_name AS alias_name1, column_name2 AS alias_name2;
SELECT column_name1, column_name2 + ', ' + column_name3 AS alias_name;

UNION: operator used to combine the result-set of two or more SELECT statements

  • Each SELECT statement within UNION must have the same number of columns
  • The columns must have similar data types
  • The columns in each SELECT statement must also be in the same order
SELECT columns_names FROM table1 UNION SELECT column_name FROM table2;

UNION operator only selects distinct values, UNION ALL will allow duplicates

GROUP BY: statement often used with aggregate functions (COUNT, MAX, MIN, SUM, AVG) to group the result-set by one or more columns

SELECT column_name1, COUNT(column_name2) FROM table_name WHERE condition GROUP BY column_name1 ORDER BY COUNT(column_name2) DESC;

HAVING: this clause was added to SQL because the WHERE keyword could not be used with aggregated functions

SELECT COUNT(column_name1), column_name2 FROM table GROUP BY column_name2 HAVING COUNT(column_name1) > 5;

UPDATE Queries

INSERT INTO: used to insert new records/rows in a table

INSERT INTO table_name (column1, column2) VALUES (value1, value2);
INSERT INTO table_name VALUES (value1, value2 ...);

UPDATE: used to modify the existing records in a table

UPDATE table_name SET column1 = value1, column2 = value2 WHERE condition;
UPDATE table_name SET column_name = value;

DELETE: used to delete existing records/rows in a table

DELETE FROM table_name WHERE condition;
DELETE * FROM table_name;

Reporting Queries

COUNT: returns the # of occurrences

SELECT COUNT (DISTINCT column_name);

MIN() and MAX(): returns the smallest/largest value of the selected column

SELECT MIN (column_names) FROM table_name WHERE condition;
SELECT MAX (column_names) FROM table_name WHERE condition;

AVG(): returns the average value of a numeric column

SELECT AVG (column_name) FROM table_name WHERE condition;

SUM(): returns the total sum of a numeric column

SELECT SUM (column_name) FROM table_name WHERE condition;

JOIN Queries

INNER JOIN: returns records that have matching value in both tables

SELECT column_names FROM table1 INNER JOIN table2 ON table1.column_name=table2.column_name;
SELECT table1.column_name1, table2.column_name2, table3.column_name3 FROM ((table1 INNER JOIN table2 ON relationship) INNER JOIN table3 ON relationship);

LEFT (OUTER) JOIN: returns all records from the left table (table1), and the matched records from the right table (table2)

SELECT column_names FROM table1 LEFT JOIN table2 ON table1.column_name=table2.column_name;

RIGHT (OUTER) JOIN: returns all records from the right table (table2), and the matched records from the left table (table1)

SELECT column_names FROM table1 RIGHT JOIN table2 ON table1.column_name=table2.column_name;

FULL (OUTER) JOIN: returns all records when there is a match in either left or right table

SELECT column_names FROM table1 FULL OUTER JOIN table2 ON table1.column_name=table2.column_name;

Self JOIN: a regular join, but the table is joined with itself

SELECT column_names FROM table1 T1, table1 T2 WHERE condition;
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